[Base] Add typedefs to ScopedPtrHashMap

Add {key,mapped,value}_type to ScopedPtrHashMap for generic operation

Review URL: https://codereview.chromium.org/173853012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252893 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252893